Hybrid automatic repeat request with feedback dependent bit selection

ABSTRACT

A multi-bit HARQ feedback is transmitted by a receiver to a transmitter. The multi-bit feedback is a function of a level of convergence reached by a decoder when the previously transmitted coded data bits were decoded. The transmitter is configured to select a set of coded data bits for a retransmission as a function of the multi-bit feedback. In some embodiments, different redundancy versions of the coded data bits may be selected as a function of the multi-bit feedback. In other embodiments, a bit puncturing or bit repetition pattern may be selected as a function of the multi-bit feedback.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/814,569, filed Jul. 31, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/405,250, filed Feb. 25, 2012, now U.S. Pat. No.9,130,748, issued Sep. 8, 2015, all of which are hereby incorporated byreference as if fully set forth herein.

BACKGROUND

The present invention relates generally to retransmission protocols forwireless communication systems and, more particularly, to the selectionof retransmission parameters for hybrid automatic repeat requestoperations in wireless communication systems.

High-Speed Downlink Packet Access (HSDPA) for Wideband Code DivisionMultiple Access (WCDMA) and Long Term Evolution (LTE) networks useHybrid Automatic Repeat Request (HARQ) at the physical layer to mitigateerrors that occur during transmission of data. In HARQ, error detectionbits or check bits are added to information bits to be transmitted. Theinformation bits with the added error detection bits are then codedusing a forward error correction code to obtain a block of coded databits. The transmitter transmits a portion of these coded bits to thereceiver in an initial transmission. The receiver decodes the receivedbits and uses the error detection bits to check for uncorrected errors.If the received data block is successfully decoded, the receiver sends apositive acknowledgement (ACK) to the transmitter over a reverse controlchannel. If the received data block is not correctly decoded, thereceiver can request a retransmission by sending a negativeacknowledgement (NACK) to the transmitter over a reverse controlchannel.

In conventional HARQ operations, a single acknowledgement bit is sentfrom the receiving terminal to the transmitting terminal to indicatewhether the transmitted data packet was correctly decoded. Typically, a“1” is transmitted to indicate successful decoding and a “0” is sent toindicate a decoding failure and to request a retransmission. TheACK/NACK informs the base station whether the data packet was correctlyreceived by the user terminal. If the data packet is correctly receivedby the user terminal, the base station can proceed with the transmissionof new data packets. In the event that the data packet is not correctlyreceived by the user terminal, the base station may either repeat theoriginal transmission or send additional coded data bits, which may becombined with the previously transmitted data bits prior to decoding.Sending additional coded data bits lowers the effective coding rate andincreases the probability that the decoder will successfully decode thecoded data bits.

One drawback of conventional HARQ is that the state of the decoder isnot considered in determining the parameters of the retransmission. Ifthe decoder is close to finding on a solution, it may need only a smallamount of additional data to successfully decode the transmitted data.On the other hand, if the decoder is still far from finding a solution,then more data may be needed. In the first case, the transmitter maysend more data in the retransmission than is needed by the decoder,which wastes resources and creates unnecessary interference. In thesecond case, the transmitter may not send enough data in the nextretransmission, which will result in increased delays.

SUMMARY

The present invention relates to Hybrid Automatic Repeat Request inwireless communication networks. In embodiments of the presentinvention, information is provided to the transmitter about the state ofthe decoder so that the transmitter can adapt retransmissions to thecurrent state of the decoder. In some embodiments, a multi-bit feedbackis transmitted by the receiver to the transmitter. The multi-bitfeedback is determined as a function of the level of convergence reachedby the decoder. The transmitter can tailor the selection of the codeddata bits for the retransmission as a function of the multi-bitfeedback.

Exemplary embodiments comprise methods of data transmission implementedby a transmitter in a wireless communication network. In one exemplaryembodiment, the transmitter encodes an information bit stream togenerate coded data bits for transmission to a receiver, and transmits afirst set of the coded data bits to a receiver during a first datatransmission. Thereafter, the transmitter may receive a multi-bitfeedback responsive to the first data transmission form the receiver.The multi-bit feedback is a function of a level of convergence reachedby a decoder when decoding the coded data bits. In response to themulti-bit feedback, the transmitter selects a second set of coded databits in dependence on the multi-bit feedback and transmits the secondset of coded data bits to the receiver during a second datatransmission.

Other embodiments of the invention comprise a transmitter configured toimplement a hybrid automatic repeat request. In one embodiment, thetransmitter includes a channel coder, a transmit circuit, and acontroller. The channel coder includes an encoder to encode aninformation bit stream to generate a block of coded data bits fortransmission to the receiver. The transmit circuit transmits a first setof the coded data bits to the receiving device during a first datatransmission, and transmits a second set of the coded bits to thereceiving device during a second data transmission. The controllercontrols the transmission by the transmit circuit. More particularly,the controller receives a multi-bit feedback from the receiving deviceresponsive to the first data transmission. The multi-bit feedbackindicates a current state of the decoder. As one example, the multi-bitfeedback may indicate or comprise a function of the level of convergencereached by the decoder when the coded data bits were decoded. Thecontroller selects the second set of coded data bits in dependence onthe multi-bit feedback.

Embodiments of the present invention enable the retransmission to betailored to the specific needs of the receiver. Consequently,retransmissions should require fewer resources on average andinterference resulting from unnecessary transmissions can be avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary communication system using hybrid ARQwith variable retransmission energy.

FIG. 2 illustrates an exemplary transmitter and receiver for a wirelesscommunication network using hybrid ARQ with variable retransmissionenergy.

FIG. 3 illustrates an exemplary transmit signal processor forimplementing hybrid ARQ.

FIG. 4 illustrates an exemplary receive signal processor forimplementing hybrid ARQ.

FIG. 5 illustrates an exemplary method of data reception using variableretransmission energy.

FIG. 6 illustrates an exemplary method of data transmission withfeedback dependent bit selection.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 illustrates an exemplary wirelesscommunication network 10 using Hybrid Automatic Repeat Request (HARQ).For illustrative purposes, the disclosed embodiment operates accordingto the Long Term Evolution (LTE) standard. Those skilled in the art willappreciate, however, that the present invention is more generallyapplicable to any type of wireless communication networks using HybridAutomatic Repeat Request (HARQ) including, without limitation, WidebandCode Division Multiple Access (WCDMA) networks and WorldwideInteroperability for Microwave Access (WMAX) networks.

The wireless communication network 10 includes one or more cells 20providing service in the coverage area of the wireless communicationnetwork 10. Although a single cell 20 is illustrated in FIG. 1, thecommunication network typically contains many cells 20. A base station30 is located within each cell 20 to provide network access to wirelessterminals 40 within the cell 20. Two wireless terminals 40 are shown anddenominated by the letters “A” and “B” respectively. Wireless terminal Ais receiving user data or control data from the base station 30 over adownlink channel and transmitting acknowledgements of the downlinktransmission to the base station 30 over an uplink channel. Similarly,wireless terminal B is transmitting control data or user data over anuplink channel to the base station 30 and receiving acknowledgements ofthe uplink transmission from the base station over the downlink channel.

The base station 30 and each wireless terminal 40 include a transmitter100 and receiver 200 as shown in FIG. 2. For downlink communications,the transmitter 100 at the base station 30 transmits control or userdata over the downlink channel to the receiver 200 at one of thewireless terminals 40. The transmitter 100 at the wireless terminal 40transmits acknowledgements of the downlink transmissions over the uplinkchannel to the receiver 200 at the base station 30. For uplinkcommunications, the transmitter 100 at the wireless terminal 40transmits data to the receiver 200 at the base station 30 over theuplink channel. The transmitter 100 at the base station 30 transmitsacknowledgements over the downlink channel to the receiver 200 at thewireless terminal 40.

The transmitter 100 at either the base station 30 or the wirelessterminals 40 includes a transmit signal processor 110, a transmitcircuit 170 coupled to one or more transmit antennas (not shown), and acontroller 180. An information bit stream in digital form is input tothe transmit signal processor 110. The transmit signal processor 110performs error coding to generate coded data bits and maps the codeddata bits to complex modulation symbols to generate transmit signals fortransmission to the receiver 200. After digital-to analog conversion,the transmit circuits 170 up-convert, filter, and amplify the transmitsignals, which are transmitted over the communication channel to thereceiver 200. The controller 180 controls the operation of thetransmitter 100 according to the applicable communication standard. Thefunctions performed by the controller 180 include HARQ control 190. Aswill be described herein, the controller 180 receives a multi-bitfeedback and determines parameters for retransmissions based on themulti-bit feedback. The multi-bit feedback includes information aboutthe state of a decoder (FIG. 4) at the receiver 200. The transmit signalprocessor 110 and controller 180 may be implemented with one or moreprocessors, hardware, firmware, or a combination thereof.

The receiver 200 at either the wireless terminal 40 or base station 30includes receive circuits 210 coupled to one or more receive antennas(not shown), a receive signal processor 220, and controller 280. Thereceive circuits 210 amplify, filter, and down-convert the receivedsignals to baseband frequency. After analog-to-digital conversion, thereceive signal processor 220 demodulates and decodes the receivedsignals. Controller 280 controls operation of the receiver 200 accordingto the applicable communication standard. The functions performed by thecontroller 280 include a HARQ control 290. As will be described herein,the controller 280 generates a multi-bit feedback for transmission tothe transmitter 100, which provides information to the transmitter 100about the state of a decoder (see FIG. 4) at the receiver 200. Thereceive signal processor 220 and controller 280 may be implemented withone or more processors, hardware, firmware, or a combination thereof.

In LTE networks, HARQ with soft combining is employed for both downlinkand uplink transmissions in order to increase robustness against datatransmission errors that inevitably occur in wireless communicationchannels. The transmitter 100 at either the base station 30 (downlink)or wireless terminal 40 (uplink) adds error detection bits or check bitsto a block of information bits to be transmitted. The added errordetection bits enable the detection of data transmission errors by thereceiver 200 at the wireless terminal 40 (downlink) or base station 30(uplink). The transmitter 100 encodes the information bits with theadded error detection bits using a forward error correction (FEC) codeto obtain a block of coded data bits. The transmitter 100 transmits someor all of the coded data bits to the receiver 200. The receiver 200decodes the received data and uses the error detection bits to check foruncorrected errors. If the received data is successfully decoded, thereceiver 200 sends a positive acknowledgement (ACK) to the transmitter100 over a reverse control channel. If the received data is notcorrectly decoded, the receiver 200 can request a retransmission bysending a negative acknowledgement (NACK) to the transmitter 100 over areverse control channel. During the retransmission, coded data bitsrepresenting the same information bits are transmitted.

In conventional HARQ schemes, a single ACK/NACK bit is transmitted fromthe receiver 200 to the transmitter 100 too indicate the results ofdecoding. The received data is discarded if uncorrected errors aredetected and the same coded data bits transmitted in the initialtransmission are repeated in the retransmission. Although the data fromthe first transmission may not be decodable, it contains usefulinformation that is lost when the data is discarded. This shortcoming isaddressed by combining HARQ with soft combining. With soft combining,the received data is saved and combined with data received during theretransmission. The combined data is then decoded.

The type of combining used can be categorized as either Chase combiningor Incremental Redundancy (IR) combining. With Chase combining, the samecoded data bits transmitted in the initial transmission are repeated inthe retransmission. Maximal ratio combining (MRC) or another type ofcombining is used to combine the data bits received in each transmissionto increase the signal-to-noise ratio (SNR) and thereby increase theprobability that the data will be successfully decoded.

With incremental redundancy, the set of coded data bits transmittedduring the retransmission does not have to be the same as the set ofcoded data bits transmitted during the original transmission. Instead,multiple sets of coded data bits are generated, with each setrepresenting the same set of information bits. When a retransmission isrequired, the transmitter 100 typically will send a different set of thecoded data bits. The sets of coded bits are referred to as redundancyversions. The receiver 200 combines the bits received in theretransmission with the bits received in the initial transmission.Because the retransmission increases the redundancy, the effective coderate is reduced thereby increasing the chances that the data will besuccessfully decoded.

Incremental redundancy is typically based on a family of codes known asrate compatible codes. Examples of rate compatible codes include ratecompatible convolutional codes (RPCCs) and rate compatible turbo code(RPTCs). Rate compatible codes a set of distinct codes that satisfy therate compatibility constraint. The rate compatibility constraintrequires that all of the coded data bits in higher rate codes are alsopart of any lower rate codes in the same family. The puncturing patternsare defined to satisfy the rate compatibility constraint.

In the first transmission, a limited number of coded data bitscorresponding to a higher rate code are transmitted. Each retransmissionprovides additional bits resulting in lower effective code rates. As oneexample, consider a rate 1/4 mother code where the bits are equallydivided into three redundancy versions. In the first transmission, only1 in every 3 bits is transmitted yielding an effective code rate afterthe first transmission of 3/4. Each retransmission adds additional bitsthat results in a lower rate code. Continuing with the same example,after the first retransmission, the code rate will be 3/8, and after thesecond retransmission the effective code rate will be 1/4.

FIG. 3 illustrates the main functional components of the transmit signalprocessor involved in HARQ operations. The transmit signal processor 110includes a channel coder 120 and modulator 160. An information bitstream is input to the channel coder 120. The channel coder 120 encodesthe information bit stream to generate a block of coded data bits. Themodulator 160 maps the coded data bits to corresponding modulationsymbols and modulates a carrier signal to generate a transmit signal,which is output to the transmit circuit 170.

The channel coder 120 includes an error detection encoder 130, a forwarderror correction (FEC) encoder 140, and a rate matching circuit 150. Theerror detection encoder 130 receives an information block (IB)containing information bits, generates a set of check bits, and appendsthe generated bits to the original information bits to generate atransport block (TB). The error detection encoder 130 may, for example,comprise a cyclic redundancy check (CRC) encoder, in which case thecheck bits may be referred to as CRC bits. The CRC bits enable thereceiver 200 to detect uncorrected errors for HARQ operations ashereinafter described. The transport block is input to the FEC encoder140. The FEC encoder 140 encodes the bits for the transport block usinga FEC code to enable correction of at least some bit errors that mayoccur during data transmission. Exemplary FEC codes applicable toembodiments of the present invention include Turbo codes, low densityparity check (LDPC) codes, convolutional codes, and block codes. The FECencoder 140 outputs a set of coded data bits, referred to herein as acode block (CB). Following FEC encoding, the coded data bits may, insome embodiments, be input to a rate matching circuit 150. Rate matchingcircuit 150 punctures or repeats some of the coded data bits to generatea specified number of bits needed to match the available channelresources. The number of coded bits output by the rate matching circuit150 is dependent upon the number of assigned resource blocks, theselected modulation scheme, and the spatial multiplexing order. Thecoded data bits from the rate matching circuit are then output to themodulator 160.

FIG. 4 illustrates the main functional components of the receive signalprocessor 220 involved in HARQ operations. The receive signal processor220 includes a demodulator 230 and a channel decoder 240. Thedemodulator 230 demodulates the received signal and outputs the codeddata bits to the channel decoder 240. The coded data bits output by thedemodulator 230 are a function of the code block (CB) output by the FECencoder 140, and include either that entire code block or a subset ofthat code block. It should be recognized that the coded data bitsreceived may contain some bit errors. The job of the channel decoder 240is to decode the received data bits to correct any bit errors that mighthave occurred and to obtain the original information bits (assuming thatdecoding errors do not occur).

The channel decoder 240 includes an FEC decoder 250 and an errordetection decoder 260. The FEC decoder 250 corrects errors that may haveoccurred during transmission using the FEC code applied at thetransmitter 100. The output of the FEC decoder 250 corresponds to thetransport block (TB) that was encoded at the transmitter 100. The errordetection decoder 260 then checks whether the decoded data stream outputfrom the FEC decoder 250 contains any uncorrected errors using the errordetection bits that were appended at the transmitter 100. The results ofthe decoding and error detection process are input to the controller280, which generates feedback that is transmitted over a feedbackchannel to the transmitter 100.

In embodiments of the present invention, instead of sending a singleACK/NACK bit as feedback to indicate the result of decoding, a multi-bitACK/NACK feedback is generated by the controller 280 and transmittedover a feedback channel from the receiver 200 to the transmitter 100 toindicate a current state of the FEC decoder 250. The additional bits inthe feedback enable the transmitter 100 to adapt the parameters of theretransmission to the current state of the FEC decoder 250. For example,the transmitter 100 may determine an amount of energy to apply to theretransmission depending on the current state of the FEC decoder 250.Also, the transmitter 100 may determine the content of theretransmission depending on the current state of the decoder 250.

The exemplary embodiments of the invention described herein are adaptedfor HARQ schemes using Turbo codes or LDPC codes. For these types ofcodes, an iterative decoder is typically used as an FEC decoder 250. Tobriefly summarize, an iterative decoder employs two component decodersthat work together to iteratively decode the applied code. The componentdecoders are both soft-output decoders. During each iteration,“extrinsic information” is output from each of the component decodersand fed to the input of the other component decoder. The “extrinsicinformation” typically comprises a log-likelihood ratio (LLR) that helpsto refine the a priori probability of the data for the next iteration.The component decoders iteratively decode the received data and worktoward the same solution. During decoding, a convergence metric iscomputed to determine how close the soft-output decoders are toconvergence. Typically, the number of iterations is preset and decodingcan be terminated early if the component decoders converge on asolution.

The specific techniques for calculating the convergence metric are notmaterial to the invention and therefore not described herein in detail.Exemplary techniques for computation of the convergence metric aredescribed in C. Bai, J. Jiang, and P. Zhang, Hardware implementation ofLog-MAP turbo decoder for W-CDMA node B with CRC-aided early stopping,in Proceedings of IEEE Vehicular Technology Conference (VTC '02), vol.2, pp. 1016-1019, Birmingham, Ala., USA, May 2002.

In one exemplary embodiment, if the decoding is not successful, theconvergence metric is output from the FEC decoder 250 to the controller280 along with a failure indication. In order to provide a multi-bitfeedback, the convergence metric computed at the receiver 200 isquantized and mapped to a multi-bit feedback. For example, assuming thatthe convergence metric comprises a value between 0 and 1 indicating theprobability of converging, the multi-bit feedback may comprise afour-bit value indicating one of four probability ranges as shown inTable 1.

TABLE 1 Mapping and Quantization of Convergence Metric ConvergenceMetric Multi-Bit Feedback   0-.24 00 .25-.49 01 .50-.74 10 .75-1.0 11

The multi-bit feedback provides information to the transmitter 100 aboutthe state of the FEC decoder 250. This information, referred to hereinas convergence information, is useful because a FEC decoder 250 that isclose to converging requires less new information than a FEC decoder 250that is far from converging. The convergence information can thus beused to tailor the retransmission to the needs of the FEC decoder 250.In some embodiments of the invention, the convergence information isused at the transmitter 100 to select the coded data bits that areincluded in the retransmission depending on the level of convergencereached by the decoder. The bit selection process takes advantage of thefact that some of the coded bits are more important than others. Forexample, with Turbo codes, the systematic bits have higher importance tothe decoder than the parity bits. Hence, the initial transmission willtypically include the systematic bits of higher importance along withsome parity bits. If the initial transmission is received with poorquality, it may be more beneficial to retransmit the systematic bitsthan to transmit additional parity bits. Therefore, HARQ schemes usingincremental redundancy can benefit from a multi-bit feedback thatprovides more information about the state of the decoder.

In some embodiments, the receiver 200 may combine the convergenceinformation with other information to generate the multi-bit feedback.As one example, the multi-bit feedback may be determined based on thelevel of convergence reached by the FEC decoder 250 and on channelconditions. A receiver 200 at a wireless terminal 40 normally estimateschannel conditions and provides channel quality feedback to a schedulerat the transmitter. A convergence metric and channel quality metric maybe weighted and combined to generate a combined metric that is thenquantized and mapped to a multi-bit feedback. As another example, areceiver 100 at a base station may estimate its current load andgenerate a load metric that is combined with the convergenceinformation, channel information or both.

The multi-bit feedback is transmitted by the receiver 200 to thetransmitter 100. The transmitter 100 is configured to select a set ofcoded data bits for a retransmission based on the multi-bit feedback. Insome embodiments of the invention, incremental redundancy is used andthe transmitter 100 selects a redundancy version of the coded data bitsfor the retransmission depending on the multi-bit feedback. This is incontrast to conventional HARQ schemes where the selection of theredundancy version is typically fixed for each transmission. Eachredundancy version comprises a different set of coded data bits. In someembodiments, each redundancy version comprises a distinct set of thecoded data bits. In other embodiments, the redundancy version maycomprise overlapping subsets of the coded data bits. Each redundancyversion may have the same number of coded data bits, or the redundancyversion may have different numbers of coded data bits. Depending on themulti-bit feedback, which is indicative of the level of convergencereached by the FEC decoder 250, the controller 180 at the transmitter100 may elect to send the same redundancy version during theretransmission, or a different redundancy version. Sending the sameredundancy version results in a petition of the previously transmittedbits, which may be more beneficial than sending new parity bits if theoriginal transmission was received with poor quality.

In other embodiments of the invention, the transmitter 100 may select apuncturing pattern or bit repetition pattern used by the rate matchingcircuit depending on the multi-bit feedback. The transmitter 100 mayhave a predetermined set of bit puncturing and bit repetition patternsfrom which to choose. Depending on the multi-bit feedback, thecontroller 180 at the transmitter 100 may select one of the candidatebit puncturing or bit petition patterns. This technique can be appliedto both Chase combining and incremental redundancy.

In the case of Chase combining, all of the bits in the retransmissionwill comprise previously transmitted bits. Some of the previouslytransmitted bits may be punctured in the retransmission according to theselected bit repetition pattern. Alternatively, some of the previouslytransmitted bits may be repeated twice in the retransmission accordingto a selected bit repetition pattern. The transmitter 100 may also use acombination of bit puncturing and bit repetition where some previouslytransmitted bits are punctured and some are repeated two or more timesin the retransmission.

In systems using incremental redundancy, it will be recognized that thedifferent redundancy versions correspond to different puncturingpatterns. If all of the puncturing patterns correspond to one of thepossible redundancy versions, selecting the bit puncturing pattern isequivalent to selecting a redundancy version. In other embodiments,however, bit puncturing or bit repetition may be applied to a selectedredundancy version. For example, if RV2 is selected, then selected bitsof RV2 can be punctured or repeated. In some embodiments, eachredundancy version may have different sets of candidate bit puncturingand bit repletion patterns. The transmitter 100 selects from among thecandidate patterns for the selected redundancy version.

Repeating or puncturing coded data bits results in a variable number ofcoded data bits in the retransmission, which in turn results in a timevarying duration for the retransmission. In systems where the resourceallocation for the retransmission is fixed, the maximum number of bitsthat can be included in the retransmission will be determined by theamount of the allocated resources. If less than the maximum number ofbits is used for the retransmission, the transmitter 100 can reduce thenumber of resource elements used for the retransmission by varying thetime duration of the retransmission, varying the number of subcarriersused for the retransmission, or a combination thereof. In code divisionmultiple access (CDMA) systems, the transmitter 100 can vary the numberof spreading codes used for the retransmission. Because no transmissionoccurs in the unused resource, interference with other users is reduced.

FIG. 5 illustrates an exemplary method 300 implemented by a receiver 200in one embodiment of the invention. The receiver 200 may be located ineither a base station 30 or wireless terminal 40. The receiver 200receives a first set of coded data bits from a transmitter 100 during afirst data transmission (block 310). The first set of coded data bitsrepresents a set of information bits in an information bit stream. Thereceiver 200 decodes the first set of coded data bits and generates aconvergence metric indicating a level of convergence reached by adecoder (block 320). The receiver 200 computes a multi-bit feedback as afunction of the convergence metric (block 330) and transmits themulti-bit feedback to the transmitter (block 340). The receiver 200 mayalso receive a second set of coded data bits representing theinformation bits from the transmitter 100 during a second datatransmission (block 350). The second set of data bits may be arepetition of the first set of data bits, or may comprise new coded databits. The receiver combines the first and second set of data bits togenerate a combined set of data bits (block 360). The combined set ofdata bits is then decoded by the receiver 200 (block 370).

FIG. 6 illustrates an exemplary method 400 implemented by a transmitter100 in one embodiment of the present invention. The transmitter 100 maybe located in either a base station 30 or wireless terminal 40. Thetransmitter 100 codes an information bit stream to generate a block ofcoded data bits (block 410). In one embodiment, error detection bitssuch as cyclic redundancy check code (CRC) bits, are appended to theinformation bits. The information bits with appended error detectionbits are then encoded using an FEC code, such as a Turbo code or LDPCcode. During an initial transmission, a first set of the coded data bitsare transmitted to the receiver 200, which may be located at a wirelessterminal 40 (downlink) or base station 30 (uplink) (block 420). In someembodiments, e.g. where Chase combining is used, the first set of codeddata bits may comprise the entire block of coded data bits. In otherembodiments, e.g. where incremental redundancy is used, the first set ofcoded data bits may comprise a subset of the coded data bits generatedduring the coding process. Subsequently, the transmitter 100 receives amulti-bit feedback from the receiver 200 which is determined as afunction of a level of convergence reached by a decoder when the codeddata bits were decoded (block 430). In response to the multi-bitfeedback, the transmitter 100 selects a second set of coded data bitsdepending on the multi-bit feedback and transmits the second set ofcoded data bits to the receiver (block 440). In some embodiments, thetransmitter may use the multi-bit feedback to select a redundancyversion of the coded data bits for the retransmission. The selectedredundancy version may comprise a repetition of the first datatransmission, or may comprise a different redundancy version withadditional coded data bits. In other embodiments of the invention, thetransmitter 100 may use the multi-bit feedback to select a bitpuncturing or bit repetition pattern to apply to a set of the coded databits. The bit puncturing pattern or bit repetition pattern can beapplied to the full set of coded data bits output by the FEC encoder, orto a subset (i.e. redundancy version) of the coded data bits.

The use of multi-bit feedback and variable bit selection depending onthe multi-bit feedback enables the transmitter 100 to tailorretransmissions to the specific needs of the receiver 200. Consequently,use of resources for HARQ can be reduced and unnecessary interferencewith other users may be avoided.

The present invention may, of course, be carried out in other specificways than those herein set forth without departing from the scope andessential characteristics of the invention. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

What is claimed is:
 1. A data retransmission method implemented at areceiver, the method comprising: receiving, from a transmitter, a firstset of coded data bits during a first data transmission; decoding thefirst set of the coded data bits; transmitting, to the transmitter, amulti-bit feedback responsive to the first data transmission, whereinthe multi-bit feedback indicates a level of convergence reached whendecoding the first set of the coded data bits; in response to themulti-bit feedback, receiving, from the transmitter, a second set of thecoded data bits during a second data transmission; combining the firstand second sets of the coded data bits; and decoding the combined firstand second sets of the coded data bits.
 2. The data retransmissionmethod of claim 1, wherein the second set of the coded data bits isbased at least in part on the level of convergence indicated by themulti-bit feedback.
 3. The data retransmission method of claim 1,wherein the second set of the coded data bits comprises one redundancyversion of the coded data bits selected from two or more redundancyversions of the coded data bits depending on the level of convergence.4. The data retransmission method of claim 3, wherein one of theredundancy versions comprises a repetition of the first set of the codeddata bits.
 5. The data retransmission method of claim 1, whereinselected ones of the coded data bits in the second set of the coded databits are punctured or repeated as a function of the level ofconvergence.
 6. The data retransmission method of claim 5, wherein theselected ones of the coded data bits in the second set of the coded databits which are punctured or repeated are punctured or repeated as afunction of a bit puncturing pattern or of a bit repetition patternselected from a predetermined set of bit puncturing and bit repetitionpatterns.
 7. The data retransmission method of claim 1, whereinreceiving the second set of the coded data bits comprises receiving thesecond set of the coded data bits over less than all of the resourcesallocated for the second data transmission.
 8. The data retransmissionmethod of claim 7, wherein receiving the second set of the coded databits over less than all of the resources allocated for the second datatransmission comprises receiving the second set of the coded data bitson fewer symbol periods than are allocated for the second datatransmission.
 9. The data retransmission method of claim 7, whereinreceiving the second set of the coded data bits over less than all ofthe resources allocated for the second data transmission comprisesreceiving the second set of the coded data bits on fewer subcarriersthan are allocated for the second data transmission.
 10. A receiver foroperation in a wireless communication network, the receiver comprising:a transceiver configured to receive, from a transmitter, a first set ofcoded data bits during a first data transmission and a second set of thecoded data bits during a second data transmission; a decoder configuredto decode the first set of coded data bits; a controller configured to:transmit, to the transmitter via the transceiver, a multi-bit feedbackresponsive to the first data transmission, wherein the multi-bitfeedback indicates a level of convergence reached by the decoder whendecoding the first set of the coded data bits; and combine the first andsecond sets of the coded data bits; and wherein the decoder is furtherconfigured to decode the combined first and second sets of the codeddata bits.
 11. The receiver of claim 10, wherein the second set of thecoded data bits is based at least in part on the level of convergenceindicated by the multi-bit feedback.
 12. The receiver of claim 10,wherein the second set of the coded data bits comprises one redundancyversion of the coded data bits selected from two or more redundancyversions of the coded data bits depending on the level of convergence.13. The receiver of claim 12, wherein one of the redundancy versionscomprises a repetition of the first set of the coded data bits.
 14. Thereceiver of claim 10, wherein selected ones of the coded data bits inthe second set of the coded data bits are punctured or repeated as afunction of the level of convergence.
 15. The receiver of claim 14,wherein the selected ones of the coded data bits in the second set ofthe coded data bits which are punctured or repeated are punctured orrepeated as a function of a bit puncturing pattern or of a bitrepetition pattern selected from a predetermined set of bit puncturingand bit repetition patterns.
 16. The receiver of claim 10, wherein thetransceiver is configured to receive the second set of the coded databits over less than all of the resources allocated for the second datatransmission.
 17. The receiver of claim 16, wherein the transceiver isconfigured to receive the second set of the coded data bits on fewersymbol periods than are allocated for the second data transmission. 18.The receiver of claim 16, wherein the transceiver is configured toreceive the second set of the coded data bits on fewer subcarriers thanare allocated for the second data transmission.